The invention relates to a method for detecting a liquid level in a container of a circuit.
In particular, the invention relates to a method for detecting a level of blood in a container of a circuit of a dialysis machine, to which the present application will make specific reference without in any way limiting the scope of the invention.
A known-type dialysis machine comprises a first blood circulation circuit and a second circulation circuit for the dialysate liquid. The first circuit and the second circuit are connected to a filter for conveying, respectively, the blood and dialysate liquid through the filter, which is provided with a semi-permeable membrane separating the blood from the dialysate liquid. The first circuit is provided with a container, known as a drip chamber, into which the blood is supplied from a first tract of the first circuit, and drips and collects on the bottom of the container, thence to enter a second tract of the first circuit. The container has the function of preventing air from becoming trapped in the blood in the form of bubbles, which might cause embolisms once the treated blood was returned to the cardio-vascular system of the patient. To guarantee the safest possible treatment the blood level in the container must be maintained within an optimum range of values, below which the possibility of creating air bubbles in the blood returning to the patient exists, and above which the pressure increases to unacceptable values which are dangerous for the patient.
To solve this problem, the prior art teaches blood level detection devices, comprising an optical emitter arranged on one side of the container and an optical reader arranged on another side of the container at an optimal level. This sensor device detects only if the level of blood is above or below the optimal level and is therefore unable to provide an accurate level reading. To obtain a more accurate blood level reading, the above-described sensor device has been modified to include two optical emitters and two optical readers suitably arranged, which provide an acceptability interval parameter of the blood level.
Still more accurate readings can be achieved with a plurality of optical emitters and a plurality of optical readers, which define a plurality of intervals and detect the interval which the blood level is at.
The above-described sensor devices are based on the principle of emission and reception of a signal and become progressively more complicated as the need for more accurate blood level readings increases, since the number of emitters and readers increases together with the need for accuracy.